Figure 10.13 Satellite systems, especially System Argos, use radio signals transmitted from surface buoys to determine the position of the buoy. The satellite S receives a radio signal from the buoy B. The time rate of change of the signal, the Doppler shift, is a function of buoy position and distance from the satellite’s track. The recorded Doppler signal is transmitted to ground stations E, which relays the information to processing centers A via control stations K. From Dietrich et al. (1980).